Mixtures of helium and oxygen are used in scuba diving tanks to help prevent the bends, which is a condition caused by nitrogen bubbles forming in the bloodstream. If 75 L of oxygen and 25 L of helium at STP are pumped into a scuba tank with a volume of 8.0 L, what is the partial pressure of oxygen in the tank?

Question

Quizplus · Accepted Answer

At STP (Standard Temperature and Pressure), 1 mole of any gas occupies 22.4 L. The total moles of oxygen are 75 L / 22.4 L/mol = 3.35 moles, and the total moles of helium are 25 L / 22.4 L/mol = 1.12 moles. The total moles in the tank are 3.35 + 1.12 = 4.47 moles. The fraction of the total moles that is oxygen is 3.35 / 4.47. The total pressure is given by the ideal gas law, P = nRT/V, but since we're looking for the partial pressure of oxygen, we can simplify this to the ratio of moles of oxygen to total moles times total pressure. The total volume is 8.0 L, and at STP, the total pressure would be 1 atm if we had 22.4 L of gas. However, we have compressed 100 L of gas into 8 L, so the compression factor is 100 L / 8 L = 12.5. Therefore, the total pressure in the tank is 12.5 atm, and the partial pressure of oxygen is 3.35 moles / 4.47 moles * 12.5 atm = 9.4 atm.

Mixtures of Helium and Oxygen Are Used in Scuba Diving